A machine plant, such as for example a power plant for generating electricity, has an electrical generator and at least one turbine, the turbine driving the generator. For this purpose, the turbine and the generator are arranged on a common shaft train. It is possible to provide couplings in the shaft train in order to couple individual turbines into the shaft train or decouple them from the shaft train.
During the operation of the power plant, the generator feeds electricity into a power grid. Electrical disturbances in the power grid may have the effect that a torsional oscillation of the shaft train is induced by the generator. In the worst case, the shaft train may be induced to oscillate at one of its natural frequencies. Being induced to oscillate at a natural frequency has the effect of high torsional stress loading of the shaft train, which may lead to a reduction in its service life or to the formation of stress cracks. It is expected that the disturbances in the power grid will occur more frequently in the future, because the structures of the power grid are changing in the course of the transition to new forms of energy.
Conventionally, the loading of the shaft train is measured, by its rotational speed being measured with high resolution at a number of axial positions of the shaft train. The loading of the shaft train is then concluded from the differences in the rotational speeds at the different axial positions. However, in this method the measuring technique and the associated evaluation are complex. It is alternatively possible to measure oscillations in the electrical energy delivery of the power plant.
In the event that potential oscillations are identified in the energy delivery, no conclusions as to the actual loading of the shaft train can be drawn however.
DE 40 32 299 A1 describes a method for monitoring a rotatable component in which the oscillation excursion of the component in the radial direction in relation to the component and the rotational position of the component are measured time-dependently. EP 0 585 623 A2 describes a method for the early detection of a crack in a rotating shaft. DE 27 34 396 A1 describes a method for monitoring torsional oscillations on shafts in which the instantaneous power of the generator is measured.